1. Field of the Invention
The present invention relates in general to a multiport underwater sound transducer and pertains, more particularly, to a transducer which utilizes multiple ported resonant chambers located on opposite sides of a driver and in which the ports resonate at two different frequencies and produce an additive output at frequencies between the resonant frequencies.
2. Background Discussion
Multiple ported loudspeaker systems for air transducers have been described previously, most notably in U.S. Pat. No. 4,549,631, by Amar G. Bose. In Bose's invention, the front and back surfaces of the loudspeaker drive two separate subchambers which are ported via tubes to the region outside the rectangular enclosure. Each chamber-port combination forms a Helmholtz resonator for the purpose of acoustic radiation. The Helmholtz resonances of these chambers are set to different frequencies yielding a nearly uniform response between the two resonances.
Helmholtz resonators are well-known in the prior art of both electroacoustic transducers (see U.S. Pat. No. 1,869,178, to A. L. Thuras, for "Translating Device", issued Jul. 26, 1932) and acoustics in general. The most simple example of a Helmholtz resonator is observed by blowing across the spout of a wine or soda bottle and hearing a tone. (For theory and other examples, see the following references: U.S. Pat. Nos: 1,969,704 and 4,628,528).
U.S. Pat. No. 1,969,704, entitled "Acoustic Device", issued Aug. 7, 1934 by A. D'Alton reveals a dual chamber, multiple tube invention with loudspeaker system response curves and precedes the patent of Bose by 41 years. The Bose patent, filed Oct. 23, 1983, does not reference a possibly related acoustic wave guide transmission patent, U.S. Pat. No. 4,628,528, filed earlier on Sep. 29, 1982 also by Bose (and Short), where a possible underwater sound application is noted.
The D'Alton invention teaches the use of multiple tubes or ports. Similarly, the Bose invention employs tubes through which the subchambers communicate to the region outside the rectangular enclosure. In addition, both loudspeaker systems do not provide for underwater sound transduction.
U.S. Pat. No. 4,413,198, entitled "Piezoelectric Transducer Apparatus", issued Nov. 1, 1983 by Jonathon R. Bost reveals a dual resonant chamber loudspeaker in which the chambers are driven by opposite sides of a piezoelectric driver. While this design provides for a broadened frequency response, relative to previous designs, there exists no underwater capacity. In addition, this loudspeaker is limited in frequency response due to relying on opposite sides of one driver to drive the chambers.
Accordingly, it is an object of the present invention to provide an improved sound transducer which can effectively operate underwater.
A further object of the present invention is to provide a multiport underwater sound transducer in which the need for using tubes to port the chambers is relieved.
Another object of the present invention is to provide an improved sound transducer which yields a smooth response.
Another object of the present invention is to provide an improved sound transducer which utilizes multiple ports with Helmholtz resonances set to different frequencies yielding an additive output response between the two resonant frequencies.
Another object of the present invention is to provide an improved sound transducer which employs separate drivers to drive separate chambers for a broad frequency response.